While federal investigators are trying to answer that, WLKY captured images that one railroad expert said point to what could be a major factor in the derailment.

Robert Comer is a national expert on railroad accidents. Over the past 24 years, he's investigated more than 300 across the country.

When the P&L train derailed, he said he spotted trouble on the track.

“There's serious problems with this track,” Comer said.

Comer, who lives hundreds of miles away, wanted to be sure.

Since the track was destroyed and replaced at the scene of derailment, WLKY’s Duane Pohlman went as close as he could and took video and pictures at the nearest intersections north and south.

“The pictures you took here show ties in bad condition,” Comer said.

Wooden ties are the foundation; they hold up the rail and the train's massive weight.

Comer said the pictures reveal serious issues.

“The ties are cracked. Some of them are actually broken where the spikes go in. This track should have been fixed a very long time ago,” Comer said. “The rotted ties and broken ties are causes of derailments because if the ties are not solid and the spikes are not solid, then the rail can move.”

Comer said there’s another issue in the pictures.

“You notice there's only one spike, but there's four holes,” Comer said. “If you're going to run a heavy train with these loaded tanker cars, very heavy, on a curve and you don't have enough spikes in to hold down plates, that means that the rail can move and if the rail moves, that's what a derailment is. It was just an accident waiting to happen.”

WLKY has repeatedly requested a response from P&L.

While the company answered many other questions, it did not directly address Comer's concerns.

In a statement, P&L stated, "Some of the cross ties in the vicinity of the derailment were replaced in 2008. P&L's capital investment, maintenance practices and inspections (visual and ultrasonic) all are designed to meet designated track class standards."

WLKY received no answer about the plates with one spike.

P&L said "The mainline (track) is inspected two times per week."

According to a U.S. Department of Transportation inventory report, 14 trains a day make their way up and down the same line and many carry the same chemicals involved in the derailment.

While WLKY’s investigation revealed one expert’s concern, it is possible something else went wrong.

WLKY has requested inspection reports from both P&L and the Federal Railroad Administration, but neither has handed them over.

P&L responded to many of WLKY’s other questions, and the investigation continues. Check back Tuesday for some never-before-seen details as WLKY dissects the derailment.

In a direct response to WLKY, P&L said its track was last inspected on Oct. 27, just two days before the derailment.

According to the company, "The mainline (track) is inspected at least two times per week."

Photos taken by WLKY of the same track near the derailment 10 days later documented cracked, split and buried railroad ties and metal plates with one spike.

“In derailment after derailment in the United States, when the track was inspected after the derailment, what was found was the ties were rotted. There were missing spikes, there weren't enough spikes in the hold down plates,” Comer said.

P&L has not responded specifically to Comer's concerns, but stated "Some of the cross ties in the vicinity of the derailment were replaced in 2008."

The company has responded to several questions we asked immediately after the derailment and explosion.

According to P&L, each car involved weighed more than 150,000 pounds and some weighed more than 200,000 pounds. Most of the weight was from the chemicals they were carrying.

The Obama administration will unveil a major climate change plan Monday aimed at a large reduction in greenhouse gas emissions from the nation's coal-burning power plants, a senior administration official told CNN.